System and method for regulating data transmission in accordance with a receiver&#39;s expected demodulation capacity

ABSTRACT

In a receiving side apparatus  150,  reception quality of receive data is measured by a reception quality measurement section  157,  receive data errors are detected by an error detection section  156,  and when an error is detected a retransmission request signal and reception quality signal are transmitted multiplexed with transmit data by a transmit frame creation section  158.  In a transmitting side apparatus  100,  when a retransmission request signal is received a capacity necessary for demodulating data in a receiving side apparatus  150  is detected from a reception quality signal by a scheduling section  110,  and data is retransmitted at that capacity. By this means it is possible to reduce the number of data retransmissions during transmission and reception, and to improve transmission efficiency.

TECHNICAL FIELD

The present invention relates to a data transmission system composed ofa communication terminal apparatus and base station apparatus in amobile communication system and a method of data transmission betweenthese apparatuses.

BACKGROUND ART

Heretofore, a data transmission system and data transmission method ofthis kind have been disclosed in Patent Publication No. 1647396.

FIG. 1 is a block diagram showing the configuration of a conventionaldata transmission system. The data transmission system shown in FIG. 1comprises a transmitting side apparatus 10 and a receiving sideapparatus 60.

The transmitting side apparatus 10 comprises a buffer 11, transmit framecreation section 12, modulator 13, transmit radio section 14, antenna15, antenna duplexer 16, receive radio section 17, demodulator 18, andseparator 19.

The receiving side apparatus 60 comprises an antenna 61, antennaduplexer 62, receive radio section 63, demodulator 64, data holdingsection 65, error detection section 66, transmit frame creation section67, modulator 68, and transmit radio section 69.

With this kind of configuration, first, in the transmitting sideapparatus 10, transmit data is stored in the buffer 11, this storedtransmit data is framed by the transmit frame creation section 12, andthis transmit frame signal is output to the modulator 13.

After undergoing modulation processing by the modulator 13, the transmitframe signal undergoes predetermined radio processing such asup-conversion by the transmit radio section 14, and after passing viathe antenna duplexer 16, is transmitted as a radio signal from theantenna 15.

Then, in the receiving side apparatus 60, a signal received by theantenna 61 is output via the antenna duplexer 62 to the receive radiosection 63, where it undergoes predetermined radio processing such asdown-conversion, and the resulting signal is output to the demodulator64.

The received signal is demodulated by the demodulator 64, and thisdemodulated receive data is held in the data holding section 65 andoutput to the error detection section 66. The error detection section 66performs error detection on the receive data. If an error is detected, asignal (hereinafter referred to as “NACK signal”) requestingretransmission is output from the error detection section 66 to thetransmit frame creation section 67.

In the transmit frame creation section 67, framing is performed thatmultiplexes the NACK signal with transmit data, and this transmit framesignal is output to the modulator 68. This transmit frame signal ismodulated by the modulator 68, and after undergoing predetermined radioprocessing by the transmit radio section 69, is transmitted as a radiosignal from the antenna 61 via the antenna duplexer 62.

This transmit signal is received by the antenna 15 of the transmittingside apparatus 10, output via the antenna duplexer 16 to the receiveradio section 17 where it undergoes predetermined radio processing, andthen demodulated by the demodulator 18 and separated into receive dataand a NACK signal by the separator 19. The receive data is output tolatter-stage receive processing circuitry (not shown), and the NACKsignal is output to the buffer 11, whereby the data previouslytransmitted from the buffer 11 is retransmitted.

This retransmitted data is received in the receiving side apparatus 60in the same way as described above, and is held combined with theprevious receive data in the data holding section 65. This held combineddata undergoes error detection by the error detection section 66.

As described above, if an error is detected, a NACK signal is output tothe transmit frame creation section 67. If, on the other hand, no erroris detected, a transmission request signal (hereinafter referred to as“ACK signal”) requesting transmission of the next data from thetransmitting side apparatus 10 is output to the transmit frame creationsection 67.

The above-described series of operations is repeated until an ACK signalis obtained in this way. When an ACK signal is obtained, the data in thedata holding section 65 is considered to be receive data, and is outputto latter-stage receive processing circuitry (not shown). Following thisoutput, that receive data is eliminated from the data holding section65.

When an ACK signal is input to the transmit frame creation section 67,the transmit frame creation section 67 performs framing that multiplexesthe ACK signal with transmit data. This transmit frame signal istransmitted to the transmitting side apparatus 10 as described above.

In the transmitting side apparatus 10, the received ACK signal is outputto the buffer 11, and the data for which that ACK signal was obtained iseliminated from the buffer 11. Then, transmission of the next databegins.

As described above, in a conventional data transmission system, receivedata error detection is carried out by the receiving side apparatus, andif an error is detected a retransmission request is made to thetransmitting side apparatus. In response to this, an operation toretransmit the same data is repeated, so that eventually there is nodata error in the receiving side apparatus.

However, with conventional apparatuses, in response to a retransmissionrequest from the receiving side, an operation that performsretransmission on the transmitting side is simply repeated until thereis no data error on the receiving side, and there is thus a problem inthat, if the retransmitted data is not appropriate, the number ofretransmissions will be large and transmission efficiency will degrade.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a data transmissionsystem and data transmission method that enable the number of dataretransmissions during transmission and reception to be decreased,thereby enabling transmission efficiency to be improved.

This object is achieved by noting that receive data can be combined, andas long as the result of combination meets a predetermined quality,receive data can be demodulated; and detecting the capacity necessaryfor demodulation, and performing scheduling at the time ofretransmission so that data is retransmitted at the capacity necessaryfor demodulation.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the configuration of a conventionaldata transmission system;

FIG. 2 is a block diagram showing the configuration of a datatransmission system according to Embodiment 1 of the present invention;

FIG. 3 is a drawing showing a reception quality transmission method fora data transmission system according to Embodiment 1 of the presentinvention; and

FIG. 4 is a block diagram showing the configuration of a datatransmission system according to Embodiment 2 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference now to the accompanying drawings, embodiments of thepresent invention will be explained in detail below.

(Embodiment 1)

FIG. 2 is a block diagram showing the configuration of a datatransmission system according to Embodiment 1 of the present invention.The data transmission system shown in FIG. 2 comprises a transmittingside apparatus 100 and a receiving side apparatus 150.

The transmitting side apparatus 100 comprises a buffer 101, transmitframe creation section 102, modulator 103, transmit radio section 104,antenna 105, antenna duplexer 106, receive radio section 107,demodulator 108, separator 109, and scheduling section 110.

The receiving side apparatus 150 comprises an antenna 151, antennaduplexer 152, receive radio section 153, demodulator 154, data holdingsection 155, error detection section 156, reception quality measurementsection 157, transmit frame creation section 158, modulator 159, andtransmit radio section 160.

The flow of data transmitted and received between the transmitting sideapparatus 100 and receiving side apparatus 150 will be described below.

First, in the transmitting side apparatus 100, transmit data is storedin the buffer 101, this stored transmit data is framed by the transmitframe creation section 102, and this transmit frame signal is output tothe modulator 103.

After undergoing modulation processing by the modulator 103, thetransmit frame signal undergoes predetermined radio processing such asup-conversion by the transmit radio section 104, and after passing viathe antenna duplexer 106, is transmitted as a radio signal from theantenna 105.

Then, in the receiving side apparatus 150, a signal received by theantenna 151 is output via the antenna duplexer 152 to the receive radiosection 153. In the receive radio section 153 predetermined radioprocessing such as down-conversion is carried out on the radio frequencyreceived signal, and a baseband received signal is output to thereception quality measurement section 157 and demodulator 154.

In the reception quality measurement section 157, the received signalquality is determined by measurement of the SIR (signal to interferenceratio), received field strength, or the like, and a signal indicatingthis received signal quality (hereinafter referred to as “receptionquality signal”) is output to the transmit frame creation section 158.

The received signal is demodulated by the demodulator 154, and thisdemodulated receive data is held in the data holding section 155 andoutput to the error detection section 156. The error detection section156 performs error detection on the receive data. If an error isdetected, a NACK signal is output from the error detection section 156to the transmit frame creation section 158.

In the transmit frame creation section 158, framing is performed thatmultiplexes the reception quality signal and NACK signal with transmitdata, and the framed signal, which is a transmit frame signal, is outputto the modulator 159.

The transmit frame signal is modulated by the modulator 159, and afterundergoing predetermined radio processing by the transmit radio section160, is transmitted as a radio signal from the antenna 151 via theantenna duplexer 152.

This transmit signal is received by the antenna 105 of the transmittingside apparatus 100, output via the antenna duplexer 106 to the receiveradio section 107 where it undergoes predetermined radio processing, andthen demodulated by the demodulator 108 and output to the separator 109.

In the separator 109, the demodulated data is separated into threecomponents: receive data, a NACK signal, and a reception quality signal.The receive data is output to latter-stage receive processing circuitry(not shown), and the NACK signal and reception quality signal are outputto the scheduling section 110.

In the scheduling section 110, a retransmission request is recognizedfrom the NACK signal, radio resources are assigned according to thetraffic conditions at the time of retransmission, scheduling isdetermined according to these radio resources and the reception qualitysignal, and retransmission is carried out using this scheduling.

Here, the scheduling section 110 finds the maximum transmission capacityof data that can be transmitted from the traffic volume at the time ofretransmission, and if the capacity necessary for demodulation isgreater than this maximum transmission capacity, performs scheduling sothat data is retransmitted at the maximum transmission capacity.

Assume, for example, that 30% of the capacity necessary for demodulationis received in the first transmission, and the reception quality signalis information indicating that a further 70% capacity is necessary fordemodulation. In this case, if there is room in the traffic, thescheduling section 110 performs scheduling so that data is transmittedat 70% capacity at one time.

However, if there is no room in the traffic, and, for example, data canonly be transmitted at 30% capacity, the scheduling section 110 willretransmit data at 30% capacity. In this case, since only 60% of thecapacity necessary for demodulation has been received at that point, aNACK signal is again returned to have 40% retransmitted. If, at thistime, data can only be transmitted at 30%, retransmission is performedagain at 30% capacity. In this way, 90% of the necessary capacity isreceived by the receiving side, and therefore 10% capacityretransmission is requested by the next NACK signal. So 10%retransmission is performed this time. Thus, in response to a requestthat exceeds the maximum capacity, scheduling is performed so that datais retransmitted at the maximum capacity at that point. In this case,the number of data retransmissions is three.

Also, scheduling need not be limited to being determined according tothe number of retransmissions in this way, but may also be determinedtaking account of a transmission method other than number ofretransmissions. An example of another transmission method is totransmit data according to any one or a combination of spreading factor,transmission rate, modulation method, coding rate, beam width, and arraydirectivity. That is to say, as well as the number of retransmissionsbeing determined according to the current traffic, the othertransmission method is changed, and scheduling is determined accordingto the transmission method after this change.

A change of spreading factor is carried out for the transmit framecreation section 102 and modulator 103, a change of transmission ratefor the transmit frame creation section 102, a change of modulationmethod for the transmit frame creation section 102 and modulator 103,and a change of code rate for the transmit frame creation section 102.Changes of beam width and array directivity are carried out when theantenna 105 has an array configuration.

Based on scheduling determined in this way, data transmitted last timein the buffer 101 is retransmitted at the capacity necessary fordemodulation.

This retransmitted data is received by the receiving side apparatus 150in the same way as described above, and is combined with the previousreceive data and held in the data holding section 155. This heldcombined data undergoes error detection by the error detection section156.

As described above, if an error is detected, a NACK signal is output tothe transmit frame creation section 158. If, on the other hand, no erroris detected, an ACK signal requesting transmission of the next data fromthe transmitting side apparatus 100 is output to the transmit framecreation section 158.

The above-described series of operations is repeated until an ACK signalis obtained in this way. When an ACK signal is obtained, the data in thedata holding section 155 is considered to be receive data, and is outputto latter-stage receive processing circuitry (not shown). Following thisoutput, that receive data is eliminated from the data holding section155.

When an ACK signal is input to the transmit frame creation section 158,the transmit frame creation section 158 performs framing thatmultiplexes the ACK signal with transmit data. This transmit framesignal is transmitted to the transmitting side apparatus 100 asdescribed above.

In the transmitting side apparatus 100, the received ACK signal is sentto the scheduling section 110. When the ACK signal is input to thescheduling section 110, the scheduling section 110 performs control toeliminate data for which that ACK signal was obtained from the buffer101, and starts transmission control for the next data. At the sametime, radio resources to be used for transmission are assigned accordingto the traffic conditions at that start time, scheduling is determinedaccording to the radio resources, and transmission of the next data isstarted in accordance with this scheduling.

Thus, the receiving side apparatus performs receive data errordetection, and when an error is detected transmits a retransmissionrequest signal and reception quality signal, and the transmitting sideapparatus identifies the capacity necessary for demodulation by thereceiving side apparatus from the reception quality signal when theretransmission request signal is received, and retransmits data at thiscapacity necessary for demodulation.

By this means, it is possible to reduce the number of dataretransmissions during transmission and reception, and improvetransmission efficiency. In other words, it is possible to prevent thedegradation in transmission efficiency due to the large number ofretransmissions resulting from simply repeating retransmissions untilthere is no data error on the receiving side in the conventional way.

Also, when data is retransmitted, the transmitting side apparatus findsthe maximum transmission capacity at which transmission is possible fromthe traffic volume at that time, and if the capacity necessary fordemodulation is greater than this maximum transmission capacity,retransmits data at the maximum transmission capacity.

By this means, data can be retransmitted efficiently even if thecapacity necessary for demodulation is greater than the transmissiblemaximum transmission capacity at the time of retransmission, andtransmission efficiency can be improved.

Moreover, when data is retransmitted, in the transmitting side apparatusthe scheduling section 110 assigns radio resources comprising variousradio communication functions according to traffic conditions at thattime so that data can be retransmitted at the greatest possiblecapacity.

By this means, a transmission method that includes number oftransmissions can be changed optimally within radio resources, therebyenabling the number of data retransmissions during transmission andreception to be reduced, and transmission efficiency to be improved.

Furthermore, in the transmitting side apparatus 100, the schedulingsection 110 may preassign radio resources to be used for transmissionaccording to traffic conditions before transmitting the first data, andtransmit according to these radio resources. In this case, when thereceiving side apparatus 150 sends back a NACK signal and receptionquality signal, the scheduling section 110 determines schedulingaccording to the aforementioned preassigned radio resources, and appliesthis scheduling until the end of retransmissions.

Also, assignment of radio resources used in transmission according totraffic conditions may be performed once for every particular chunk ofdata—that is, every certain number of transmissions of packet data.Moreover, it is also possible to perform radio resource assignment onlyat the time of initial data transmission when transmission of all packetdata is performed.

By these means, it is possible to eliminate processing for deciding onradio resources when retransmitting, and to reduce overall apparatusprocessing. Furthermore, since individual channels can be extended,scheduling can be carried out in an unrestricted fashion withoutconsidering other users.

Also, it is possible to perform reception quality measurement only thefirst time an error is detected. In this case, the first receptionquality signal sent to the scheduling section 110 is stored, andthereafter, that stored reception quality signal is used as it is untilthe end of retransmissions. In addition, reception quality measurementmay be performed at a rate of once per predetermined number of times. Inthis case, a reception quality signal sent to the scheduling section 110is stored, and thereafter, that stored reception quality signal issequentially updated for use.

By this means, reception quality measurement by the receiving sideapparatus can be reduced, enabling lower receiving side apparatus powerconsumption to be achieved. This is especially useful when the receivingside apparatus is a communication terminal apparatus.

Furthermore, when determining scheduling at the time of datatransmission, a configuration may be used whereby reception quality forthe previous data is referenced. That is to say, in the transmittingside apparatus 100 the scheduling section 110 stores the receptionquality signal for the previous data. When an ACK signal is sent andtransmission of the previous data ends, transmission of the next data isstarted. At this time the scheduling section 110 assigns radio resourcesto be used for transmission according to the stored reception qualitysignal and the traffic conditions.

For example, if reception quality is good and retransmission is notnecessary, transmission is performed with radio resources reduced to alevel at which demodulation can be performed at one time. To be morespecific, assuming that in initial data transmission the receiving sideapparatus 150 receives at 120% of the capacity necessary fordemodulation, in transmission of the next data, transmission will beperformed at 10/12 of the capacity of the previous time so that data isreceived at 100% of the capacity necessary for demodulation.

On the other hand, if reception quality is poor, transmission isperformed with radio resources extended to a level at which demodulationcan be performed at one time. For example, assuming that in initial datatransmission data is received at 30% of the capacity necessary fordemodulation, and the remaining 70% capacity transmission is performedby retransmission, enabling demodulation to be achieved, in transmissionof the next data, transmission will be performed at 10/3 of the capacityof the previous time so that data is received at 100% of the capacitynecessary for demodulation. However, this applies only to the case where100% transmission is permitted within the radio resources. If, forexample, transmission within the radio resources is only permitted at upto 80% of the capacity necessary for demodulation, it will be determinedthat the next data is to be sent at 80%, followed by retransmission at20%.

By using the previous reception quality signal in initial datatransmission in this way, it is possible to transmit data with anoptimal transmission method including number of retransmissions even ininitial transmission.

In the above description, the transmit frame creation section 158performs framing by independently multiplexing the reception qualitysignal and the NACK signal/ACK signal with transmit data. However, thepresent invention is not limited to this, and it is also possible forthe transmit frame creation section 158 to perform processing so thatthe NACK signal has information indicating reception quality, and toperform framing by multiplexing the post-processing NACK signal/ACKsignal with transmit data.

For example, there may be three kinds of NACK signalrepresentation—“N1”, “N2”, and “N3”—according to the reception quality,with representation as four states (two bits) together with the ACKsignal “AC”. Then the three kinds of NACK signal will be differentiatedas follows: “N1” when reception quality is comparatively good anddemodulation will be possible on reception of a signal of a little morecapacity (for example, 0 to 25%); “N2” when reception quality is good,and a signal of a certain level of capacity (for example, 25 to 50%) isnecessary for demodulation; and “N3” when reception quality is poor anda signal of considerable capacity (for example, 50% or more) isnecessary for demodulation.

FIG. 3 is a drawing showing the reception quality transmission method inthis case. FIG. 3 shows transmit packets A to E, reception quality atthe time of transmission of those packets, and a NACK signal/ACK signalrepresented by four states based on reception results. The width of atransmit packet indicated by a rectangle shows the size of the capacity.

FIG. 3 shows the case where an error is detected in packets B and E andthe other packets are received correctly. The propagation environmentwhen packet B is transmitted is comparatively good, and the propagationenvironment when packet E is transmitted is poor.

In the case shown in FIG. 3, the receiving side apparatus transmits “N1”to the transmitting side apparatus to request retransmission of packetB. The transmitting side apparatus determines that a further 25%capacity is necessary for demodulation, and retransmits packet B(B_(R1)).

The receiving side apparatus also transmits “N3” to the transmittingside apparatus to request retransmission of packet E. The transmittingside apparatus determines that a further 75% capacity is necessary fordemodulation, and retransmits packet E (E_(R1)).

It is herein assumed that the receiving side apparatus receives packetE_(R1) but is not able to demodulate the packet because the capacity isnot quite sufficient. The receiving side apparatus then transmits “N1”to request retransmission of packet E once again. The transmitting sideapparatus determines that a further 25% capacity is necessary fordemodulation, and retransmits packet E (E_(R2)).

If framing is performed by multiplexing with transmit data a NACK signalor ACK signal that has information indicating reception quality in thisway, it is possible to reduce the transmission of signals other thantransmit data compared with the case where a reception quality signaland NACK signal/ACK signal are simply multiplexed with transmit data,and thus to improve transmission efficiency.

Also, if the number of kinds of NACK signal is a power of 2−1, thenumber of kinds of signal together with the ACK signal is a power of 2,and therefore this is convenient for performing binary digitaltransmission.

(Embodiment 2)

FIG. 4 is a block diagram showing the configuration of a datatransmission system according to Embodiment 2 of the present invention.Parts in the data transmission system shown in FIG. 4 identical to thosein FIG. 2 are assigned the same codes as in FIG. 2 and their detailedexplanations are omitted.

The data transmission system shown in FIG. 4 differs from that in FIG. 2in having a separator 251 and scheduling section 252 added to thereceiving side apparatus 250.

With this kind of configuration, first, in the transmitting sideapparatus 100 the scheduling section 110 assigns radio resources to beused for transmission according to the traffic conditions beforetransmit data is transmitted, and outputs a radio resource signalindicating information on these radio resources to the transmit framecreation section 102.

In the transmit frame creation section 102, framing is performed thatmultiplexes the radio resource signal with transmit data, and thistransmit frame signal is transmitted.

This transmit frame signal is received by the receiving side apparatus250, and after being demodulated by the demodulator 154, is separatedinto data and a radio resource signal by the separator 251. Thisseparated data is held by the data holding section 155 and output to theerror detection section 156, and the radio resource signal is output tothe scheduling section 252.

In the scheduling section 252, when a NACK signal is input in the eventof error detection, scheduling within assigned radio resources isdetermined based on the reception quality signal and radio resourcesignal, and a scheduling signal indicating the scheduling result and aNACK signal are output to the transmit frame creation section 158.

In the transmit frame creation section 158, framing is performed thatmultiplexes the scheduling signal and NACK signal with transmit data,and this transmit frame signal is transmitted.

This transmit frame signal is received by the transmitting sideapparatus 100, and is separated into three components by the separator109: data, a NACK signal, and a scheduling signal.

The NACK signal and scheduling signal are output to the schedulingsection 110, where retransmission control is performed according to thescheduling indicated by the scheduling signal.

Data retransmitted in accordance with this control is combined with theprevious data and held in the data holding section 155, and thiscombined data undergoes error detection by the error detection section156. Thereafter, the above-described series of operations is repeateduntil an ACK signal is obtained.

When an ACK signal is obtained, the data in the data holding section 155is considered to be receive data, and is output to latter-stage receiveprocessing circuitry (not shown). Following this output, that receivedata is eliminated from the data holding section 155.

The ACK signal is input to the transmit frame creation section 158 whereframing is performed that multiplexes the ACK signal with transmit data,and the resulting signal is transmitted to the transmitting sideapparatus 100.

In the transmitting side apparatus 100, the received ACK signal is sentto the scheduling section 110 where control is performed to eliminatedata for which the ACK signal was obtained from the buffer 101, andtransmission control for the next data is started.

At the same time, in the scheduling section 110 radio resources to beused for transmission are assigned according to the traffic conditionsat that start time, a radio resource signal indicating information onthose radio resources is multiplexed with the next output to form aframe by the transmit frame creation section 102, and this transmitframe signal is transmitted.

Thus the transmitting side apparatus 100 preassigns radio resources tobe used for transmission based on the traffic conditions before datatransmission, and transmits information on these radio resources. Thereceiving side apparatus 250 finds the capacity necessary fordemodulation from the reception quality when a receive data error isdetected, and determines scheduling information for retransmitting datawithin the radio resources indicated by the above-mentioned information.The transmitting side apparatus 100 then retransmits data based on thatscheduling information.

By this means, it is sufficient for data necessary for demodulationfound on the receiving side to be retransmitted from the transmittingside, enabling the number of data retransmissions during transmissionand reception to be reduced and transmission efficiency to be improved.

As is clear from the above descriptions, according to the presentinvention the number of data retransmissions during transmission andreception can be reduced and transmission efficiency can be improved bydetecting the capacity necessary for demodulation, and, at the time ofretransmission, performing scheduling and retransmitting data at thecapacity necessary for demodulation.

This application is based on Japanese Patent Application No. 2000-150507filed on May 22, 2000, and Japanese Patent Application No. 2001-078466filed on Mar. 19, 2001, entire content of which is expresslyincorporated by reference herein.

INDUSTRIAL APPLICABILITY

The present invention is suit-able for use in a communication terminalapparatus and base station apparatus in a mobile communication system.

1. A data transmission system comprising a transmitting side apparatusthat transmits data and a receiving side apparatus that receives data,wherein: said receiving side apparatus measures the reception quality ofreceived data and transmits, if an error is detected in the receiveddata, to said transmitting side apparatus a retransmission requestsignal corresponding to the measured reception quality, wherein thecorrespondence is such that a plurality of retransmission requestsignals transmitted in response to detected errors are differentiatedaccording to respective measures of reception quality; and saidtransmitting side apparatus detects, upon receiving the retransmissionrequest signal, a capacity necessary for demodulation at said receivingside apparatus, based on the reception quality corresponding to thereceived retransmission request signal, and determines a capacity fordata retransmission based on the detected demodulation capacity andtraffic conditions, wherein the total number of reception qualitymeasures that may differentiate the plurality of retransmission requestsignals is a number one less than a power of two.
 2. The datatransmission system according to claim 1, wherein said transmitting sideapparatus finds a transmissible maximum transmission capacity intraffic, at a time of data retransmission, and if the detected capacitynecessary for demodulation is greater than this maximum transmissioncapacity, retransmits data at said maximum transmission capacity.
 3. Thedata transmission system according to claim 1, wherein said transmittingside apparatus assigns radio resources so that data is retransmitted ata transmissible maximum transmission capacity in traffic at a time ofdata retransmission.
 4. The data transmission system according to claim1, wherein said transmitting side apparatus preassigns radio resourcesto be used for transmission before data transmission and uses theseassigned radio resources until retransmission of one transmit unit ofdata ends.
 5. The data transmission system according to claim 1, whereinsaid transmitting side apparatus preassigns radio resources to be usedfor transmission before data transmission and uses these assigned radioresources for a selected number of data units or for the transmissionand all retransmissions of a data unit.
 6. The data transmission systemaccording to claim 1, wherein all retransmissions of particular datareceived in error are transmitted at a capacity based on the measuredreception quality of the original transmission of said particular data.7. The data transmission system according to claim 1, wherein apredetermined number of retransmissions of particular data received inerror are transmitted at a capacity based on the measured receptionquality of the original transmission of said particular data.
 8. Thedata transmission system according to claim 1, wherein said transmittingside apparatus assigns radio resources according to traffic at the timeof data retransmission and transmits, within said radio resources, dataat a capacity that compensates for an excess or deficiency of measuredreception quality at the time of a previous data transmission.
 9. A datatransmission system comprising a base station apparatus and acommunication terminal apparatus, wherein: said communication terminalapparatus measures the reception quality of received data and transmits,if an error is detected in the received data, to said base stationapparatus a retransmission request signal corresponding to the measuredreception quality, wherein the correspondence is such that a pluralityof retransmission request signals transmitted in response to detectederrors are differentiated according to respective measures of receptionquality; said base station apparatus detects, upon receiving theretransmission request signal, a capacity necessary for demodulation atsaid communication terminal apparatus, based on the reception qualitycorresponding to the received retransmission request signal, anddetermines a capacity for data retransmission based on the detecteddemodulation capacity and traffic conditions; and the total number ofreception quality measures that may differentiate the plurality ofretransmission request signals is a number one less than a power of two.10. A data transmission method comprising: at a receiving sideapparatus: measuring the reception quality of received data, detectingwhether the received data has an error; and transmitting, if an error isdetected in the received data, to a transmitting side apparatus aretransmission request signal corresponding to the measured receptionquality, wherein the correspondence is such that a plurality ofretransmission request signals transmitted in response to detectederrors are differentiated according to respective measures of receptionquality, and at the transmitting side apparatus: receiving theretransmission request signal transmitted by the receiving sideapparatus; detecting a capacity necessary for demodulation at areceiving side apparatus, based on the reception quality correspondingto the received retransmission request signal; and determining acapacity for data retransmission based on the detected demodulationcapacity and traffic conditions, wherein the total number of receptionquality measures that may differentiate the plurality of retransmissionrequest signals is a number one less than a power of two.